Continuous process for making adipic acid



mesa-d Feb. 27, 1940" m Q 2,191,786

j UNITED STATES PATENT OFFICE CONTINUOUS PROCESS FOR MAKING ADIPIC ACIDAlbert M. Aronow, Los Angeles', Calif., assignmof one-flfthto C. A.Miketta, Beverly Hills, Calif.

No Drawing. Application March 18, 1938,

. Serial No. 196,747

.9 Claims. (Cl. 260-531) This invention relates to a process ofmanuwhereby continuous manufacture of adipic acid facturing adipic acidand alkyl adipic acids in in a facile and economical manner is assured.an eflicient and rapid manner. It is particularly These and otherobjects and advantages of the directed to a process in which conditionsof -adpresent invention will become apparent to those dition and mixingof reagents, concentration, skilled in the art from the followingdetailed 3 etc., permit continuous operation and production descriptionof exemplary forms-of procedure. of high yields. In starting theprocess, a body of reaction solu- Adipic acid is an aliphaticdicarboxylic acid tion is formed in a reaction zone, this reaction,which has been made heretofore by oxidation of. solution containing 5%to 14% or preferably 6% l0 cyclohexanol with a'strong oxidizing acidsuch as to 10% of nitric acid, and a small amount of a lo chromic' ornitric acid. The prior processes incatalyst preferably derived of ametal capable volved boiling of a mixture of cyclohexanol and of changesin valence. Vanadium, mercury copnitrlc acid, for example, or the slowaddition of per and molybdenum are examples. These .cyclohexanol to abody of concentrated nitric metals, their oxides or salts may be presentin acid. The oxidizing reaction is exothermic and from about 0.02% to1.0% by weightof the rereadily becomes dangerously explosive. Alactionsolution. The reaction zone in which the though some adipic acid isformed by these prior solution is-formed (and maintained) may be anybatch processes, large amounts of succinic and suitable form ofapparatus provided its contents other acids are also formed and theprocesses can be thoroughly agitated and maintained at are tsatisfactory. a predetermined temperature. A kettle provided I Thepresent invention is based upon the diswith heating and cooling coils, avalved discovery that the formation of succinic acid, eta. chargeoutlet, agitators and a hood or cover can be effectively prevented orrendered inconthrough which gaseous reaction products may sequential andlarge yields of adipic acid obbe let oil. is satisfactory. Separatemeans for g m d m t ad, by carrying out theoxidizing regulated feedingof cyclohexanol, concentrated 2 reaction under controlled conditions andin a nit c id and a i ional t lyst to the bo y continuous manner, ofreaction solution should also be provided.

Generally stated, the process of this invention Since the form ofapparatus used is not a part comprises forming an acid solution andmainof this invention and the various elements are taining a lowconcentration of oxidizing acid well known to chemical engineers, theywill not 80 therein at all times, the cyclohexanol and conbe describedin detail. centrated acid being'then continuously added to The reactionsolution above defined is heated the solution and the reaction liquorcontinuousto 60 C.- preferably to we n about ly withdrawn. The volume o!the mixture in the C- and C- The DrOduCtiOn 0f p c aci reaction zone ismaintained in excess of the volis then initiated .by t e e ul tedaddition of 85 ume of reaction liquor withdrawn per minute. cyolohexanoland concentrated nitric acid. The amounts of cyclohexanol and acidintronitric acid maybe used although to 70% duced into the bqdy 1n thereaction zone are suf- 801d 1.8 preferred; The body Of reaction solutionilclent to cause oxidation and also maintain the 18 maintained inthorough tat on and t 4 desired low acid concentration in the body ofacid is added in amount sufficient to 40 abluuon. Temperatures aremaintained within bine with and oxidize the added cyclohexanol certainlow ranges as heremaner more swim and leave the desired concentration ofacid in cally set forth. Yields on the order of 95% of the actionmixture leave 5%14% or 6%-10% acid content in the body of reaction thezgz are by following such solution. Additional catalyst may also be fedto 45 I the reaction zone, say at the rate of about 0.3 It an of thisinvention thereforeto gm. per mol. of cyclohexanol, although this ratioM1056 and provide a continuous process for the can be materially variedwithout aifectlng the manufacture of adipic acid and alkyl adipic acids.resulting oxidation in a i ifi ant manner. The 0 Another object is toprovide cond t which temperature of the reaction mixture is mainso, prmit the produ of h yields of d p tained within-the desired range 0.4050. acid with a minimum concomitant production or C. C.) during theperformance of the of lower dicarboxylic acids. process.

A further object is to disclose and provide con- After the operation hasbegun as above stated. ditions of concLntration, temperature and timevirtually continuous withdrawal of the reaction .5

action mixture is correlated to the rate of addition of the reagents so"that a substantially constant volume of reactionmixture is maintained inthe reaction zone. The time during which reagents remain in the reactionzone will vary withthe volume of the body kept in the reaction zone andthe rate of addition. Reaction time need not exceed one minute so thatthe volume of the body can be equivalent to the average volume ofreagents added per minute. Control of temperature in the reaction zoneis facilitated when the reaction time is increased and larger body ofreaction mixture is maintained in the reaction zone. For this reason thevolume of the body of solution kept in the zone is preferably in ex-.cess of the volume withdrawn (or added) per minute, for example, five ormore times the I volume of the cyclohexanol and nitric acid added perminute, this assuring ample contact and reaction time.

The reaction' generates nitric oxide which can be collected and used.The reaction zone maybe kept at atmospheric or superatmosphericpressure, pressures being generally only sufilcient to assure steadyaddition of reagents and such scrubbing of the reaction gases as may bedesired. When superatmosph'eric pressures are employed,

I the temperature before referred to is to be increased in proportion tothe pressure employed herein.

The reaction mixture withdrawn from the reaction zone is allowed to coolor is chilled to atmospheric temperature or to a temperature sufficientto precipitate the adipic acid which is then separated from the motherliquor in any suitable manner, as sedimentation and decantationfiltration, centrifugal separation, etc. Chilling to about 30 C. ortherebeiow is advantageous. The mother liquor, containing between 5% and14% of nitric acid, is sent to a still (preferably of the continuouscolumn type) where it can be concentrated to 40% or higher nitric acidcontent, the water being discarded. This concentrated mother liquor isthen preferably chilled to precipitate a further amount of adipic acid.Upon removal of the adipic acid, the concentrated acid liquid can berecycled to the. reaction zone for use as a source of nitric acid infurther operation of the process.

In practice, yields of adipic acid amounting to 90% to 95% of thetheoretical are readily obtained. A body of the reaction mixture ispermitted to remain in the reaction zone when the process isdiscontinued, this body being available for use the nexttime the processis started. The adipic acid produced may be purified in any suitablemanner, as by recrystallization from water or any suitable solvent, suchas acetone methyl ethyl ketone, etc.

It is to be understood that the process of this invention is not limitedto the use of cyclohexanol since various alkyl substitution products ofcyclohexanol may be .used, these producing various alkyl adipic acids.The mode of operation herein disclosed is applicable to the manufactureof such alkyl adipic acids without material modification.

I claim: 7

1. A continuous process for manufacturing adipic acid comprising:forming abody of reac- 93, tion solution containing from about 6% to 10%of nitric acid, and a metallic catalyst ina reaction zone, said body ofreaction solution being at a temperature of between about 70 C. and 85(3.. said catalyst being of a metalhaving a variable valency,continuously adding to said body of reaction solution cyclohexanol andconcentrated nitric acid, while energetically agitating the same, inproportions suficient to. oxidize the cyclohexanol and still maintain aconcentration of from 6% to 10% of nitric acid in the reaction solution,continuously withdrawing the reaction mixture from said reaction zone ata rate correlated to the rate at which cyclohexanol and nitric acid isadded to said zone, the rate of withdrawal being adapted to permitoxidation of added cyclohexanol and maintain a body of reaction solutionin said zone, the volume of body of reaction mixture maintained in saidreaction zone being not less than five times the volume of reactionmixture withdrawn per minute, maintaining said reaction mixture at atemperature of between about 70 C. and 85"v C. in said reaction zoneduring said continuous addition and withdrawal, chilling the withdrawnreaction mixture to a temperature below 30 C., separating theprecipitated adipic acid from the acid mother liquid, distilling. saidacid mother liquid to remove water therefrom, chilling said concentratedmother liquid to precipitate further adipic acid I therefrom,'removingthe precipitated adipic'acid,

and reusing the residual concentrated mother liquid in cyclicoperationof the process- 2. A continuous process for manufacturing adipic acid,comprising: forming a body of reaction solution containing from about 6%to 10% of 'nitric' aci'dand a metallic catalyst in a reaction zone, saidbody of reaction solution be ing at a temperature between about C. and V;C.,- said catalystbein'gbf a" metal having .a

variable valency, continuously addingto said body of reaction solutioncyclohexanol and con centrated nitric acid, while energeticallyagitatingthe same, in proportions sufficient'to oxidize thecyclohexanol-and still maintain a concentration of from 6% to 10% ofnitric acidin the reaction solution, continuously withdrawing reactionmixture from said reaction zone at arate correlated to the rate at whichcyclohexanol and nitric acidis added to said zone, the rate ofwithdrawal being adapted to permit oxidation of" added cyclohexanol andmaintain a bodyo! .re--

action solution in said zone, maintaining said reaction mixture at atemperature of between about 70 C. and 85 C. in said reaction zoneduring said continuous addition-and withdrawal chilling the withdrawnreaction mixture, and separat- --.ing the precipitated adipic acid fromthe-acid mother liquid.

3. A continuous process of making adipic acids which comprises: forminga bodyof-reactionsolution containing from about 5% to 14% of nitric acidand a catalyst in a' reaction zone," saidlbody of reaction solutionbeing heated toa temperature of between 60 C. and 0., continuouslyadding to said body of reaction solution .with agitation cyclohexanoland concentrated nitric acid in proportions sufllcient to oxidize thecyclo hexanol and still maintain a concentration of from about 5%-to 14%of nitric acid in the reaction solution, withdrawing reaction mixturefrom said reaction zone at a rate correlated to the rate at whichcyclohexanol and nitric; acid is added to said zone, the rate ofwithdrawal being adapted to permit oxidation of added cyclohexanol andmaintain a body of ,reaction solution in said zone, maintaining saidreaction mixture at a temperature of between about 80 C. and 105 C. insaid reaction zone during said continuous addition and withdrawal,chilling the withdrawn reaction mixture to a temperature suiiicient toprecipitate adipic acid therefrom, and separating the precipitatedadipic acid from the acid mother liquid.

4. A continuous process of making adipic acids which comprises: forminga body of reaction solution containing from about 6% -to 10% of nitricacid and a catalyst in a reaction zone, said body of reaction solutionbeing heated to a temperature of between C. and 105 C., continuouslyadding to said body of reaction solution with agitation cyclohexanol andconcentrated nitric acid in proportions suflicient to oxidize thecyclohexanol and'still maintain a concentration of from about 6% to 10%of nitric acid inv the reaction solution, withdrawing reaction mixturefrom said reaction zone at a rate correlated to the rate at whichcyclohexanol and nitric acid is added to said zone, the rate ofwithdrawal being adapted to permit oxidation of added cyclohexanol andmaintain a body of reaction solution in said zone, maintaining saidreaction mixture at a temperature of between about 60 C. and 105 C. insaid reaction zone during said continuous addition and withdrawal,chilling the withdrawn reaction mixture to a temperature suflicient toprecipitate adipic acid therefrom, and separating the precipitatedadipic acid from the acid mother liquid.

5. In a continuous process of making adipic and alkyl substituted adipicacids, the step of continuously oxidizing a member of the groupconsisting of cyclohexanol and alkyl substitution products thereof at aconcentration of from about 4% to 14% of nitric acid and at atemperature of between 60 C. and 105 C.

6. In a continuous process of making adipic and alkyl substituted adipicacids, the step 01' continuously oxidizing a member of the groupconsisting of cyclohexanol and alkyl substitution products thereof inthe presence of a suitable catalyst at a concentration of from about 4%to 14% of nitric acid and at a temperature of between C. and C.

'7. In a continuous process of making adipic and alkyl substitutedadipic acids, the step of continuously oxidizing a member of the groupconsisting of cyclohexanol and alkyl substitution products thereof inthe presence of a suitable catalyst at a concentration of from about 6%to 10% of nitric acid and at a temperature of between 70 C. and 85 C.

8. In a continuous process of making adipic and alkyl substituted adipicacids, the steps of: forming a body of reaction solution containing anoxidizing acid in a reaction zone, continuously adding -a member of thegroup consisting of cyclohexanol and alkyl substituted products thereofwith agitation to said body of reaction solution, continuouslyintroducing an oxidizing acid into said reaction zone in quantitysufflcient to maintain oxidizing conditions in said reaction zone, andcontinuously withdrawing the reaction mixture containing adipic acidfrom said reaction zone at a rate correlated to the rate of additions tosaid zone so as to maintain a body of reaction solution in said zone.

9. A process for the production of adipic acid which comprisescontinuously introducing cyclohexanol into a nitric acid-containingsolution maintained ata temperature between 70 C. and C, maintaining theconcentration of the nitric acid in said solution between 5% and 14% bycontinuously introducing fortifying nitric acid,

continuously removing the crude reaction mixture and recovering adipicacid therefrom.

ALBERT M. ARONOW.

